Protective device



Dec. 5, 19.50 E. c. BRILL 2,532,285

PROTECTIVE DEVICE Filed July 8, 1949 2 Sheets-Sheet 1 @M MWWLWMW Dec. 5, 1950 E. c. BRILL 2,532,285

PROTECTIVE DEVICE Filed July 8, 1949 2 Sheets-Sheet 2 (P (P Q (P Q a? @l 5/4/ g ma/wbcw EVERE TT C BRL/LL Patented Dec. 5, 1950 UNITED STATES v`-PA'I,ENT 'OFFICE 7' PROTECTIVE' DEVICE Everett C; Brill, Granby, Conn., assigner of onehalf to .lamesv G. Schnell, Granby, Conn.

ApplicatiolrJuly 8, 1949, Serial No. 103,660

.i 19 '.Claims. 1

This application is a continuation-in-part of vmy copending lapplicationSerial'.l\lo; 414,.led

January S, Qlifnow abandoned.

The present invention -relates generally to electrical control means more particularly, to an electronic device responsive to variations in voltage current inputs to al1-electrically operated means andk adapted to function when. the

-power consumptionoi such means as evidenced by said inputs departs from a predetermined value.

i particularly advantageous use of the device oi the present invention is as a protective mechanhm ior use in connection with electrically operated machinery as, for example, to interrupt the operation of the machinery when the current and voltage input to the driving motor is indicative oi overload` conditions.

A principal object of the presentinvention is to provide a device which is responsive to both thea f voltage and current input to an electrically'operated means and which will correlate these values so as to function thedevice when one of these valuesdeparts from a predetermined normal in relationship to the other value.

A more specific object: of? the invention is to provide a device which will derive a voltage component having a predetermined relationship to the current input of an electricallyfoperated means and a second voltage'componentfhaving a predetermined relationship to the voltage-input of said means, and which will function as,.for

' example, to energize a protective circuit, when said components depart from a relationshipand -value corresponding to anormal relationshipiand which-may be a protective circuit-.and/orivisualor audible signalingor indicating devices,-orany other similar means desired, lwhenthe power lconsumption of a given?electricallypowered'zinstru- -mentaiity exceeds apredeteri .ined normalglvhe device one whichfcombines means for:l develop- AinfT voltage `components responsive to line volt- -age-and current,rrespectively, and means responsive-to such developed voltage components or -'energizingorotherwise actuating the auxiliary v`means. A salient` featureA ofthe device isthe Adevelopmentoi voltage components responsive to line voltage and current, respectively, which voltcomponents will vary with respect to each Aother in relationship which is different from that existing between the line voltage and line cur- 1ent to lwhich they are responsive.

This new relationship permits'sensitive and accurate functioning o the means responsive to the developed voltage components, whereby even very slight deviations from normal line current and voltage `may be detected.

As mentioned above, a principal use, forexample, to which the device of the present inl vention is particularly adapted, is in the proteci damage the apparatus being driven.

'tionv of machinery driven by electric motors from operation under overload conditions which might In such a use, the device is connected to the power lines y goingto thermotor and is preferably arranged to protect the apparatus from damage by interrupting yits operation such as by disconnecting the motor ronrthe line, disengaging a clutch the drive between the motor and apparatus, or applying a brake'etc., or any combination of these.` t is desired that the operation of the -c'gevicashall occurrimm'ediately and accurately whenlthe overload condition reaches a predeter- `mined value for, which the device has been set.

--In such an installation, the power input to the Ielectric motork is a function of the load on that motor and, therefore, the power input can be as anl indication'and measurement; of motor load conditions.

For example, if vthe in- :stallationin which the electric motoris .utilized is-.rsuchthat underv normal operating conditions there results a given vpower. consumptionby ,the ctricniotor, then it is very likely that there is an overload on the apparatus beingdriven bythe electric,motoiliunoniany material increase over that given vpower consumption.

"*lhe power input to the motor is, of course, a

hdirect function. of the .voltage and the current `in nts to theinotor.' If the volage input to the A.then

l made `motor were tot remainconstant, such as where there would be a non-fluctuating ,line voltage, a -satisactory protective device could be to function in response to current changes fonly sincethe amount of ycurrent input would thcnsbedirectly indicative of the load conditions. Hower/er;` awconstant linefvoltage is :practically never encountered in commercial installations. In actual practice, some line voltage variations always occur and in some cases they may range as high as i%.

Assuming that the motor is operated under constant load conditions but under iluctuating line voltage conditions, there will then result fluctuations in the line current suiilcient to keep the power input substantially constant. However, the changes in line current to provide a constant power input under fluctuating voltage conditions will not bear a straight line relation: ship to the voltage variations. As will be readily apparent, the change in line current will be inversely in proportion to the changes in line voltage in accordance with the formula This means, for example, that a drop in line voltage will result in a 331/3% increase in current, a 50% drop in line voltage will result in a 100% increase in current, etc. In other words, under constant load conditions, a plot of current against voltage is non-linear and in the form of a hyperbolic curve.y

To further complicate the matter, the motor eciency will vary over a wide range depending on the inp-ut voltage. In general and assuming a constant load, motor efficiency will be greater when the power input is obtained by an increased voltage and decreased current than when the power input is obtained by a decreased voltage and increased current. For very sensitive operations, these variations in motor eiciency must also be taken into consideration. The plotted curve showing the normal relationship of current and voltage, with or without correction to take into account the eiiiciency deviations just mentioned, will be referred to herein as the performa-nce curve for the motor or other device to be protected.

There are available various protective devices which can be made to function in response to line current and line voltage or a plurality of Voltage components related to said current and voltages. However, al1 of suchk instrumentalities are responsive to the arithmetic sum of these components or at least a combination thereof which does not reect the hyperbolic relationship actually existing between line voltage and line current going to an electrically operated device such as an electric motor which is operated under constant loa-d. Accordingly, when such instrumentalities are utilized, they normally will be set for such great changes in power input that they Will lack the necessary sensitivity for immediately detecting an overload condition and initiating the protection of the motor. On the other hand, if they are not set for such broad variations, they Will tend to function at times when there actually is no overload condition.

In accordance with the present invention, I have discovered that the disadvantages of the prior art of protective devices may be overcome and there may be produced a protective device having very surprising selectivity and other desirable operating characteristics by developing two voltage components in response to line current and line voltage respectively, which voltage components are modified at the initiation or thereafter so that they vary in a relationship which is different from that between the line current and line voltage, and in a relationship which can cause accurate and sensitive functioning of the protective device.

The principle underlying the present invention, therefore, is to develop voltage components for operating the protective device which are responsive to line voltage and line current, respectively, but which are not in the usual direct ratio thereto. The actual relationship desired is one corresponding to the hyperbolic performance curve heretofore referred to. By way of more specific example, and to assist in the understanding of the invention, it usually is desired to cover line voltage variations between '75% and 115% of normal; i. e., between 165 and 253 volts for a rated voltage of 220, and between the 330 and 506 volts for a rated voltage of 440. To provide the desired nonlinear relationship between the line voltage and the developed voltage component responsive thereto, the developed voltage must increase at a decreasing rate as the line voltage is increased from the lower to the upper limit. Taking the change of line voltage from 165 to 253 (88 volts) as the change from 165 to 220 volts is then 62.5% of the total. In a conventional straight line relationship between line voltage and the developed voltage component responsive thereto, the voltage component would also increase 62.5% of its total change. However, in order to'obtain a hyperbolic curve relationship between the voltage component and line voltage suitable for most installations, for example, the developed voltage component should increase to 71.875% of its total change, when the line voltage varies only 62.5% of its total change. Then when the line voltage increases for the remaining 37.5% of its total change, the developed voltage will increase only 28.125 of its total change.

Once the above principle is appreciated, various instrumentalities may be designed by one skilled in the art to accomplish the result desired. However, in order to disclose the best manner of practicing the invention but without desiring to be limited specically thereto, I have set forth in the drawings and in the description thereafter two preferred ways of constructing a device embodying Jthe invention.

Referring to the drawings:

Fig. 1 is a wiring diagram of a protective device rembodying the present invention which is .adapted to be connected into the power input line of an electric motor and to energize a protective circuit for removing the motor from the line and/or otherwise to protect the apparatus driven by the motor when the current and voltage in the lines indicate that the apparatus is being operated under overload conditions. In this specific embodiment, the development of a voltage component which does not bear a straight line relationship to line voltage is accomplished in the transformer stage of the device.

Fig. 2 is a wiring diagram of a similar protective device wherein the development of a voltage component which is not in straight line relationship to line voltage is accomplished in the amplication stage.

Referring to the drawings, and particularly to Fig. 1 thereof, the specific embodiment of the device of the present invention is illustrated as consisting of two separate units A and B. The unit A is preferably located adjacent the drive motor (not shown) so that leads from the motor starter to the motor can be conveniently connected thereto. The unit B may be mounted in any other convenient location preferably away from any excessive vibration, splashing oil, dirt,

aussage?,

Jetc. `An auxiliary' control isadapted'tc-be utilized `for protecting the apparatus driven by the motor by such `expediente as disengaging they motor from the line, actuating a disengaging clutch between the motor and the'drivenapparatusor by reversing the motor, `orV applying a brake`,etc., or any combination of such expedients. 'The-actual mechanism' of -thev auxiliary `control `will loe-readily understood by one skilled'lin the'art'and does not in itself form. a part o'the present-invention; accordingly; it has been shown merely dia-grammatically at C.

"I The unit Acomprises a' transformer "it 'for developing a secondary voltage responsive'to line .current and apair oi' transformers i I and I2 `connected in series for developing a'secondary7 Y"voltage responsiveto -liner voltage. 'In" the comn mercial embodiment of theinvention illustrated 'in the drawings,V for examplejthe tramsfornfiers I i and l2 may beutilized with a line' rated at either `220 'or 440 `volts and transformer-'ie vwith `'line currents ranging as high as 1GO amps. Itwilibe noted that the transformer i@ is provided with twoprimarywindings i3 and ifi. The primary windingl. is adapted to be'connected-in one or" 'the power lines whenthe linercurrent is'in a lOWer'range', for exampleycf G to 10 amps. while the'primary'winding I 3 is adapted to be connected inthe :line when `the line current varies-within a .higherranga for example, from to larnps. "The ksecondary'l of transformer it be connected across-eitheiresistor It or resistor il depending upon-the settingr of switch iB. rEhe particular resistor selected is one which will cause a voltage drop of upon the average line current and the primary Winding utilized. Terminals 2e and 2i are also connected across the resistori or il by'switch` IS so'that thevoltage developed across the particular resistor selected will appear at terminals 2li .and 2|.

AsA will be well understood by one skilledin "the art, 'the voltage component appearing `at terminals 2&3 and ZI will be in straight' line relationship to the magnitude of line current.

The transformer II is provided with a splitv primary denoted at 22 and 23, and transformer I2 is provided with a split primary denotedat 24 fand 25.'. The primaries are arranged for con- 'nection in' series across the power vlines going'to the motor (not shown). primary sections 22 Hand'23 andV primary sections 24. andZl-'i vare themselves connected in series or .parallel depending upon the position of themnltiple gpole, double throw switch 26. In the `position of `the LNswitclzi'fZtsloown in the i'irimary 4sections are in series.

As will be apparentythe setting of switch 25 as shown in the drawings is utilized for a higher line voltage such asin a conventional volt instailation, for example, lwhereas the other setting of switch 25 would be utilized for one halfv that line voltage such as a f 220 volt installation in the specific example.

'Theisecondaries of transformers Il and| I2 are connected inseriesbut in opposition to each other The transformer it suitable magnitude depending tioned above. The transformers Il and'IZcan be readily designed to accomplish'this result. v*Forv example, but withoutintending` to limit the scope of the invention thereto, I have Afoundthat satisfactory`4 resultsI can beA obtained -inmost installations by 4constructing-thev transformer \Ii with a split primary, each-'section-of-which is wound with S200 turns, and a'secondary having f 6001 turns, and by constructing ltransformer -I2 with a split primary, each section of'fwliich consists'ofr 250 turns andy with a ysecondary-consistingl of V1675 turns.

While it isfnotdesired to be limited to any particular theory of operation, thefollowing explanation is oiered of the operation of'transformers I i and I2 in order to clarify the understandingor Uvthis embodiment` of-the invention.

vThe impedance'of the primary of transformer ii is much greaterv than the impedance of Vthe primary V'of transformer I2, which'has'iewerturns, so-'that it, principally, will'control the 'amount of'primary current ofthe transformers. "This current vwill ybe a low value with no load or a very-'light secondary load. Since transformer i2 has a small number of primary turns, the ux producedby vthesmali number of ampere-turns will be small and consevquently the'voltage across the'secondary will Abe small even though this transormer-haa step-np ratio.

' to saturation of the iron.

The'characteristics of electrical steel are such that at very low values of ampere-turns, a given vincrease in ampere-turns will produce a smaller straight 'line portion of the curve whilectransformer I2- operates in the lower portion.

As the current'in the primaryof the transformer I2 increases then the flux-produced by it will increase at an increasing rate. Thesecondary voltage will also increase in the same manner. At the same time, the phase angle be- `tween primary voltageand current also varies formers.

This is true to a much greater extent in the case of transformer I2 as compared with transformer II. At low values of ampere-turns, the'inphase component of current which supplies the .l2 loss "due tothe ohmic resistance of the winding and the iron (hysteresis and eddy current) losses is small. Thequadrant component which produces the flux, however, is also small. As the rimary current is increased, the inphase component increases but the quadrant' component increases to a much greater degree. Therefore,'there is a vast difference between the primary voltage Vas well as the secondaryvoltage of the Vtwo trans- The two transformers being connected in opposition, it will be realized that the secondary voltage of the combination'increases at a decreasing rate as the primary voltage is increased over the working range.

" Accordingly,l by proper design of the trans-- formers II `and I2, it is possible to obtain a desired hyperbolic relationship between'the` developed voltage component appearing across teryrninals 2l and 2S and the line voltage. The variablesarethe amount and type of iron utilized in both transformers., the relationship between primary and secondary turns and wire sizeof both 'traiisformers',` 'the relationship between" the two primaries as to turns and wire size, the relationship between two secondaries as to turns and wire size, and the load across the secondary of the transformers.

While the foregoing embodiment utilizing the transformers Il and l2 constructed as described above is believed to be the best arrangement for obtaining the desired hyperbolic relationship between the developed secondary voltage and the line voltage in the transformer stage, other methods of obtaining this same relationship at this stage are equally feasible and would be readily apparent to one skilled in the art. For example, it is possible by proper selection of a core material, such as nickel, iron, or the like, to design a transformer which will reach magnetic saturation at a rate comparable to the desired secondary voltage curve. It also is possible to obtain similar results by the use of suitably designed magnetic shunts. For example, it is possible to provide a shunt for by-passing a portion of the ux around the secondary winding at an increasing rate as the flux produced by the primary is increased (by increasing primary voltage). Also, magnetic shunts may be designed tc cause magnetic saturation in the secondary portion of the iron as the flux is increased. It is also feasible to utilize shorted or other auxiliary windings to cause either magnetic saturation or to set up an opposing flux. Regardless of the exact method utilized, the purpose in this embodiment of the invention is to obtain a secondary voltage having the desired hyperbolic relationship to line voltage.

Terminals 2 and E3 are connected by lines 29 and 29 to a conventional filtered half-wave rectifier circuit comprising the diode 3U, lter ca pacitor 3 l resistor 32 and potentiometer 33. As a result, an adjustable unidirectional voltage directly proportional to the combined secondary voltage of transformers H and i2 is obtained between terminal S4 and the adjustable contact of potentiometer 33'. Resistor 32 is utilized merely to permit a less critical adjustment of potentiometer 33.

Terminals 2Q and 2i are connected by lines S5 and 36 to a second conventional filtered halfwave rectiiier circuit comprising diode 33, lter capacitor 39 and potentiometer til. As a result, an adjustable unidirectional voltage directly proportional to line current and varying in straight line relationship ther with is obtained between terminal 4| and the adjustable contact of potentiometer 4B.

For operation of the unit B, there is provided a conventional D.C. power supply circuit; namely, a voltage-regulated filtered full-wave rectifier circuit comprising the power transformer 45, twin-diode @6, filter capacitor Gl, resistor 4B and glow-tube voltage regulators G9 and 55.

The split primary of power transformer C consisting of sections i2 and lid is adapted to be connected with its sections in series or in parallel across a conventional 60 cycle power supply. Such a power source is indicated by the lines 52 and 5S connected to terminals 54 and 55, respectively. When the power source is an ordinary 230 volt supply, the primary sections will be connected in series as shown in solid lines in the drawing. If the supply is a conventional 115 volt source, the primary sections will be connected in parallel as shown in dotted lines, in which case the connection between terminals i3 and 133' is omitted. Line 56 connects one side of the primary section 42 to terminal 55 while line 5l connects the opposite side of the primary section 44 to the terminal 5ft through switch 5S and protective fuse 59. An indicator lamp 55 is connected across one of the primary sections, such as section iifto show when the unit is turned on by switch 58.

Secondary winding 5l is utilized to supply the power for the filament E61 of rectifier 46. Secondary winding 62 is the main winding for producing a 300 volt supply for use in operating the unit. Secondary winding 53 supplies the power for the nlaments of the remaining tubes in the circuits.

A Voltage divider circuit comprising resistors 65 and 66, and potentiometer 61 is connected across the 30G volt lines @S and e@ of the rectified power supply and in parallel with a second voltage divider circuit comprising resistor 1E! and potentiometers 'H and 72. These voltage divider circuits provide biasing potentials for use as hereinafter explained. Line F3 is provided to maintain allowable potential differences between cathode and filament of all tubes supplied by the secondary winding 63.

The auxiliary electrical control C, which has been previously described, is connected to the terminals 'i6 and l1. Terminal 'il is connected to the terminal 55 and hence to the power source line 53. Terminal 76 is connected by line 80 through protective fuse 'i9 to a double throw, double-pole switch 82 which normally is in the position shown in the drawing thereby normally connecting line 85 to terminal 86. When switch 82 is thrown to its other position, line 85 is connected through normally closed push button switch iii to terminal 'i5 which in turn is connected to terminal 56 which is connected to power supply line 52. Accordingly, when the switch 82 is moved to the other position from that shown in the drawing, the auxiliary control C will be connected directly across lines 52 and 53 and thus will be energized to perform its protective function such as stopping the motor, etc., as previously described.

The switch 32 is adapted to be operated by a solenoid Si which is connected at one end through switch 88 to the plate 89 of a gas-filled tetrode or thyratron 9i?. The other side of the solenoid S1 is connected through line 9| to the positive side of the voltage regulated full-wave rectifier circuit previously described. Cathode 55 of thyratron QQ is connected to ground as is the midpoint of discharge tubes 59 and 5B. Thus, it will be seen that the thyratron is placed under a plate voltage of volts and when this tube discharges, the solenoid 8l is energized to cause the closing of the switch 82, thereby initiating the operation of the auxiliary electrical control C.

The thyratron eil has a conventional screen grid 9'! and control grid 98. The screen grid 91 is adapted to be placed under a negative voltage While the control grid 98 is adapted to be placed under a positive voltage with respect to the cathode 55. Assuming that the plate voltage on the thyratron is suicient to cause the tube to trigger, but that the grid voltages are adjusted so i as to just prevent triggering, it will be apparent age to control grid voltage which will just trip or cause @the -.-thyratron .-:to 1 .discharger-v is `.-.linear.. By.. way of speci-o example, lbut withouti-ntention tolimit the invention thereby'. it may-.be .stated-.thatH in a commercial-type-.ofthyratron.operating at a plate -voltage of-1150-volts,fa control grid .voltageof-abeut-r@ about f--lvl l volt-can. bevoiset-hy decrease -o'iv iappro.ri-mately 4 volts inthe control grid voltage so as 13o-preventA the thyratronfromdischarging:

A portion :of the .negative voltage appearing across the potentiometerfd (which varies linearly with .respect :,to f the line current)- is impressed-on the'grid-.I-Illlv of the triode-IIlI.. this.- connection bee..

ing by line |02 extending to the..adjustablecon nected'- by lgine I (i3-to Ithe'.unfit-able .cont-act of- .por-:ff The movable Contact `.of :poten-f tentiorneter.` 1 tiometerV 'i2 in .turn-is connectedby=.. line1 |05 to the-cathodeV I of the triode lili.: In this way,

a positive taken. from Iithe- .potentiometers '.f I 1 and 12 vis superimposed-.on sthe .-.biastaken' from the potentiometer 4t. By suitably fad-- justing these three.,ptentiometers,-. the .bias ion ther-grid. mi? can-bevery closely regulated-such.' that-fthe grid-bias.-will--fall. within -thedesired. ran-ge --and l that -iiuctuation-t fin grid Abias.--.-will.-.-

bec-of a desired-magnitude?.- Theplateecurrentoutput of triode IBI, when operatedein the-proper operating region-:- will e .varyA linearly -with :respect to -theecurrentein fthe power lines-:going tog-the".V

motor :beingprotected. z

The iplate 01 off-the-...triode-IG I- is connected-- through.resistors-M8,and --I 21 .to the positivefsideofthe rectiied--power .circuit previously described-.- It thus-.wil-lbe understood .thatthe triodeI 0 I has` anapplied@ plate.- voltage .-oiy approximately v30) vol-tsl. and the. Iplate'- load resistanceonthisz 'tube may be predetermined bythe resistance-'ofthe re-fsistors |08=.-and;-,I 2-1.- .-.Resis-tor -I21.-is connected to the `tscreen grid 91a onthe thyratron i 90 through currents-limiting resistor-:I I.- r The zcircuit-icon.- stants--employedaresuc-h that the voltage drop across resistor-v |212; is greaterfthan.- the --vol-tagefprovided,- across.glow-.discharge tube illy-:theref- -VC-lts.- and a. screenf grid .vol-tage. of.. s a screen grid voltage decree-sect;-

by, `resulting ein. the --desirede .-negative'.--vo1tage on-screen grid .91. 1 .As..will. be apparent; an irl-..- creaseein line current in-.the power linesvgoingto the-.motorof-theapparatusbeing protected-,will-be accon1panied-..by..a proportionate increasein vthenegative grid.. bias on triode-l09,:-therebydecreasing. fthe .plate current .of- .-triode...|. I. and causing 1- screen grid bias of thyratron 9|! to-.become.less..

negative; f Thisrdrop. in .the negativescreen. currentobiasof thyratron..|0..is .in-.straight-linere--,

lationship to the increasesin .currentfinputto the` v motor beingprotected.

Asprevious-ly.. mentioned, .the .vol-tage` across.. potentiometer. 33..bears.a desired hyperbolic` re.--

lationship rto changes-rin -line- .voltage going fto .the

protected.y motor,... A portion. of rthisi; voltageg.,v

namely,- that.betweerr the .-adiustable., Contact of potentiometer-33..and terminal..34..is applied as..

a -negativegrid voltage ..to-..t1'ie.grid II5 @fithetriode.--| |I.thr.ough` linef-I I1 Line ,-I I8. extends.. from :terminar-3G. tothe Amovable zcontact of tentiome-terlbthus superi-mposing a positivebiasbetween the` grid.|.| Sand-cathode |23. By, proper setting-icithe-ipotentiometers.-@land 33a desired plate .-.currentr .output ontrio ed I canreadily be..

provided. It will be apparent. .that-an-increase in.. liner-.voltagez kayincreasing the-negativebiasyWi-ll decrease-theoutplltrof-triode titi. As -in the: case;y

previouslyrreferred. to... Seriesresistors I |9- and.. determine the load on this triode .I i6 and .thusdetermine its operating characteristics.-

Resistor-.|20- is connected through current.- limiting resistor |22 to.the control grid 98,-..,the cathode-96 beingconnectedto the midpoint. bef.. tween glow discharge tubesv it and. 53- In .this-.- case-.the circuit is designed so thatthe 1vo1tage acrossresistor |253 is less than the voltage across... glow tube 42 so that the resultingor combined bias .on control grid 98 is positive. As .a result,

ari-.increase in line voltage going to the motor of theaapparatus `to..be protected will cause .a der., crease inthe .plate current output. of.t1iode..l|6. whichin turn causes-.an .increase in a positive. direction of they control grid bias of the thyratron.- byf..reasony Aof .the decreased voltage drop. across :i

resistor. .I 2 I) The .screenfgrid 9 1 vis adapted to be connected-- bythe normallyopen .switch |48. to the .rnid

Whenthe switch.-

point of resistors and 66. I40-is closed-,it is assured that the thyratronwill nottrip, .this-.by reason of the resulting. .increase in the negative screen-gridvoltage.. Switch |40-- l is .operatedin unison with switch 88 by solenoid... |25. Solenoid...-|25,.is .adapted to .be operated eitherbya remote `reset switch E or an adjacent..

normallyopen push button |25. As will be apparent,remote=reset swi-tcnE and push button.-. switch,.|.26 are connectedv on oneside .to terminal.. S510-f: powersupply. -lineand on the othersideto.- solenoid...|25. The oppositeside of Solenoid .|25.. is connected to mwen-through line .|3.,.going to.

thev primary of transiormer-45. When either the remote resetsWitch-E or the adjacentresetswitch 52% areclosed.. therebvenergzing solenoid I25,.: the. :switches Vv88 and-.|40 are. movedto the other.` position fronrthat shown in -the ,drawing..and,. plac.es.resistor ySittin the plate-circuit of..the. thyratr.on....Resistor .Il-- is suiiiciently large...to insure, that. the thyratron .wil-lstop discharging. thus de...energlzing..the solenoid 81,=permitting .the switch ,82. to .more .to .the .position .shown in .the

drawingr .whereby `the auyiliarycontrol lC -is .der

. energized. Resistor and.capacitorl stabilize the .voltage acrossglow tube'. 49... Capacitors92;

93 andll may. also bel provided to .overcomesurgeswhich might. occur. in the circuits..r Capacitor..

aidsnresetting..

Iflit is .desired ftotest .the apparatus .without energizingtheauxiliary control C,.this may be accomplished by depressingthe normally closed push-buttonl which-opens the auxiliary control C .circuit..l'f..the device .is operating properlythe ,-throw. of: switch B2 willestablishconnection.. to `.the-lamp; 84.- thus giving a visual `indication If desired an overload may be placed on the motor or ma. chinery being Yprotected by. manual-meansor. any other convenient manner inorder to test the.

thatthe thyratron has discharged.

sensitivity andproper vfunctioning, -of thedevice.

drawing..

Referring toFig.- 2 ofthe .drawings showing V4a second. embodiment ofthe inventionV wherein the.. modication. of .the developedf.voltagesds ...ac-.

complished in the amplification stage, the device, in general, is very similar to that set forth in Fig. 1 described above. As in the case of the ernbodiment shown in Fig. l, the device is constructed in two units A and B, the former for use adjacent the motor being protected, and the unit B for remote installation at any convenient place. As in the previous embodiment, the device is utilized to energize an auxiliary control mechanism denoted at C.

In the sub-unit A, there is provided a current transformer 2li! having a primary 2|4 for connection in series with the motor being protected in one of the power lines going to the motor. The

secondary 2|5 is connected across resistor ZIB. The voltage drop across resistor 2|6 appears at terminals 220 and 22 As in the case of the first embodiment, the voltage appearing at terminals 220 and 22| varies linearly and in direct proportion to the amount of current going to the motor being protected.

Transformer 2|| is utilized to derive a secondary voltage responsive to the voltage on the lines going to the motor being protected. kThe transformer 2|! is provided with two primary windings 222 and 224 for connection in series or parallel across the motor power lines. The primary windings 222 and 22d are connected in series for a high power line voltage, such as 440 Volts, and are connected in parallel with the line voltage in half that amount, for example, 220 volts. The voltage induced in secondary 212 is impressed across terminals 221 and 228.V

Contrary to the method utilized in the rst embodiment of the invention, the transformer 2| I is a conventional voltage transformer and is utilized to develop a secondary voltage which varies linearly and in direct proportion to line voltage. Accordingly, the voltages appearing across terminals 220 and 22| and across 221 and 228, respectively, will vary inversely to each other in hyperbolic relationship in the same manner as the current input and voltage input of the electric motor driving the apparatus being protected when operated under constant load.

As in the rst embodiment. the voltage appearing across terminals 228 and 22| is rectied by the circuit comprising diode 238. lter capacitor 239, and potentiometer 248. Similiarly, the voltage at terminals 221 and 228 are rectified by the circuit comprising diode 230. filter capacitor 23|, resistor 232 and potentiometer 233.

As a result of the circuits so far described, there is derived a voltage drop across terminal 241| and the slidingr contact of potentiometer 240 which is aV unidirectional voltage in direct linear proportion to line current and there is derived a voltage drop across terminal 'fif and. the slidingr contact of potentiometer 233 which is in direct linear relationship to line voltage.

Also, as in the previous embodiment, a separate D.C. power supply is providing for operating unit B consisting of power transformer 245, twin diode 246, lter capacitor 241, resistors 248 and 248', and glow-discharge tubes 249 and 250. The primary 242 is connected to .terminals 255 and 254 to which are connected power supply lines 253 and 252, respectively, which power lines may be a Aconventional 120 or 220 volt supply. A switch 258 is provided to open or close the connection to primary 242, and there is also included a PTO tective fuse 253. A lamp 260 is connected across primary 242 to indicate when the unit is turned on. The power supply circuit above described is connected to a voltage divider, one leg of Whll'i comprises resistors 255 and 266 and potentiometer 261, the other leg of which comprises resistor 210 and potentiometers 21| and 212.

As in the previous embodiment, the voltage drop appearing across terminal 2M and the movable contact of 245 is impressed along with a positive voltage taken from potentiometers 21| and 212 on the grid 300 of the triode 30 I. The voltage drop across terminal and the sliding contact of potentiometer 233 is impressed along with a positive voltage derived at the movable contact of potentiometer 261 as a negative biasl on grid 3|5 of triode 3|5. The triodes 30| and 313 are operated under a plate voltage of 300 volts, as in the previous embodiment.

The plate 301 of the triode 33| is connected through series resistor 308 to the positive side of the rectified power supply circuit and a resistor 309 is connected in shunt between the plate 301 and the cathode The volta-ge drop across resistor 308 is applied to the screen grid 291 of the thyratron 290 through current limiting resistor 3 0.

In the case of triode 3| 8, the plate is connected through resistor 315 to the positive side of the power supply, and there is also provided a shunt resistor 323. Resistor 3|9 is connected through current limiting resistor 322 to the control grid 298 of the thyratron 290.

The adjustment of potentiometers 240, 21| and 212 and the amount of load provided by resistors 308 and 303 is so selected that the tube 30| is operated in the region where the plate current of tube 30| varies directly or linearly with respect to the voltage developed across potentiometer 240. Therefore, the voltage drop across resistor 308, which is created by the ilow of plate current of tube 30|, varies directly with the line current of the motor being protected.

The adjustments of potentiometers 233 and 261 and the selection of resistors 3|9 and 320 is such that the tube 3|8 is operated in the non-linear portion of its plateI current vs. grid voltage curve. The operating region is such that the plate current of tube 3|0 varies hyperbolically in relation to the voltage across potentiometer 233 in the same manner that the line voltage varies hyperbolically with respect to line current of the motor being protected. Accordingly, the voltage drop across resistor 3 I 3. which is developed by the 110W of plate current through tube 3|6, varies hyperbolically with respect to line voltage of the motor being protected.

Upon discharge of the thyratron 290, the

solenoid 281 is actuated thus closing the double pole, single throw switch 282. One arm of the switch 282, when moved to closed position, connects one side of the lamp 284 to terminal 254. The other side of lamp 284 is connected through protective fuse 219 to terminal 255. The other arm of switch 282, when moved to the closed position, connects terminal 254 through normally closed push button 28| to terminal 211, which, in turn, is connected to the auxiliary control mechanism C. The auxiliary control mechanism C is also connected through terminal 216 and fuse 219 to terminal 255. It thus will be appreciated that, when the switch 282 is moved to the closed position, which occurs when the thyratron discharges, the lamp 284 and the auxiliary control mechanism C are energized.

The auxiliary control mechanism C may also be actuated, if desired, by an auxiliary switch D which performs the same function as switch 282 namely, to connect terminal 211 to terminal 254.

open, "thus de-energizingthe auxiliary'eiectrical 1 151 control '0.'. At' the same time, the..;closing .ofa switch-33t` places .a resistor. 32lfin parallel'wii'fhr; the :potentiometer 240, thus yincreasing the negaev tive-bias on screen grid Zt'lwhich eiiectively'pre` vents the'i thyratron from'. discharging rwhile '20:

normal#L operations are being resumed.' A -re` mote reset switch denoted at E may be connected-f to terminalsilzl and-'285'. to perform the same function as pusnbutton switch326'; f

Intorderto assist inthe-understanding of'the 25 inventicnithe'folio-Wine? 'anxexjolanatinn of the mode fcf'operation'of: the specinc embodiments of-sthe"presentzinvention: If itlis assumedthatthe motorfofthe .apparatus to be: protect-ed is operV ating under normal load at a given'linev current 30l and linelwoltage'and tha-teit is desired toenergize the protective'circuitf whenthe loa'diincreases by 10%', .the circuits"areaadjusted'rso 'that'. at said f givenY 'ezvoltageg anincrease ofsloin line currentwill"decreasethe negative screen gri'dbias 35.l

on the thyratroniust suici'entto cause thethyratron to trip, Assuming thezizolta'ge remains constant; theiincreas'eiinline currentwill, of course, bena measureiofthe increase inload; By the use offh'e present'inveutionf'this amor'ntfof increase .40 in fline: 4current'nill theiea-fteialways .trip the' device regardless of line voltagechanges. This'is explained by `the factfthata change in vlinefyoltage. f

is accompanied by two'- counter-balancing func-1 tions-of the fdevice; Assuming, for simplicity of 4,5 illustration; v"that thew lineA Voltage varies' hyperV` bolicallly to causestrai tfline changes in line-x. current 'in theV reverse4 direction(performanceV curve), these straight line changes incurrent will produce straight lineffrchanges inthe negativen() screen. grid biasfoffithe thyratronf; .Thisfollowsfbecause'a voltaire is inducedby-the AcurrentF transformer :which varies instraightline relation-- shin to line current, and this inducedvoltagepis vL ampiiedifin straight line Onlinear relationship. 55.

At the-'same time,v theunmerbolic changesin line" Voltagewill produce' straightline changes'in the positive' control grid bias of 4the thyratrorr;l This follows' because." inrthe: irst Yembodiment, 'the'. transformers utilizedi'for inducing'a secondary 60 voltage .responsive to line voltage intoA a secondary voltage -change v.varies .hyperbolically with respect. to linevoltage;v .Inrthe secondiembodirrient;'the Voltagetransformer induces-:a secondary'voltage. f which Varies infstraightflinerelationship to lline'fG- voltage :but'this is lmodiiied theampliiicaticn stage-ito-fdevelop a `voltages.which varies hyperbolically'with.respectitolinevoltage; By proper adjustmentv of the-magnitude of'the changes in screen'grid. biasoi the .thyratronA as compared :70 with' Hthe changes inizccntrol ygrid bias. these changes neutralize each other andrtheibalancerotr thelthyratron remains uneiie'cted. s Therefore, the

line current abovetnormal. f

which. is requirecttoz tripthe' dei/ice is :the :.samexf75.

14 f regardless fof. :line voltage.' ..If. desired, .thesame f: eect 'could be obtained, of course, by varying the control grid bias linearlywith respect to line volt- Y age and then varying the screen grid bias hyper.l bolically with respect to line current.

To state. it another. way, the circuits are so adjustedthat a change `in line` voltage which will cause unit changes in current will cause uniform increments or vdecrements in the voltage across or-lresistors IIS and 319, respectively. Accordingly,

the total bias on the control grid of the thyratron will become more positive in uniform increments as the line'voltage increases along the hyperbolic performance curve and will become less positive in. uniform decrements as the line voltage decreases along such curve. By proper. amplication, the amount of said increments or decrements in the positive bias on the controlA grid of the thyratron may be made proportional to the increment or decrement in the -negative'bia-s on-the screen grid of the thyratron in accordance .with the firing characteristics of the thyratron.

In thespecic example given previously by WayV of illustration, the increments or decrements in l positive on the control grid of the thyratron would have to be 'four times the amount of the said increments or decrements in the negative bias' of the screen grid of the thyratron to keep the. conditions on the" thyratron in equilibrium. Asa result, the thyratron will trip only when the current and lvoltage inputs to the motor of the apparatus being protected departs from the per- Y formance characteristics of that motor; i. e., at a percentage increase in current input above the performance curve for the actual voltage input. In other words, regardless of the actual terminal voltageof the motor. (Within practical limits) the mechanical load upon the motor must increase just enough to causethe current taken by the motor to be greater bya predetermined amount above the normal current for thatl voltage in order to cause the thyratron to trip.l

Ineach of the embodiments specificallyl describe-dabcve, a negative voltage is applied to the screen grid of the thyretron which is a function of the current in the power lines going to the electric motor to be protected-while there is impressed a positive Voltage on the control grid of the thyra tron Which. is a function of the voltage on the. power lines going o the protected motor. The relationship between the screenV grid negative Voltage and the current in the power lines, on the one hand, and the relationship between the control grid. voltage and-the voltagein thevpowcr lines,y on the other, is such that thethyratron will dis charge when the current andvoltage in the pow-er lines going'to the. protected motor depart from the performance. curve. for the motor.l In the first specific embodiment, this been accompli-shed linfthe transformer stage by inducing a voltage which is non-linear with respect' to -line voltage. v .In the second embodiment, ithe 'same result has been accomplished inthe amplification stage yby non-linear ampli.; cationv ofa voltage which is responsiveV to line-voltage. It'would be equally feasible in either "ase-to `utilize a developed voltage ich varies linearly throughout with respect toline voltage and a developed volt age varying 'hyperholically with respect to line Y current, thefend'result being the-same in either i* CaSe.

rFliermistor materials or' other current, voltage or ternperaturesensitivel lmaterials alsof may be 1 used-to supplement theiuncti'on rit-the transformers. orampliiying tubes ortoimpart .the-dee.

sired characteristic thereto. Such materials may be used in numerous ways in the circuits, for example, in the plate or cathode circuits of the amplier tubes or as the load across the secondaries of the transformers, when used in the plate circuit of the ampliiier tubes, for example, a resistor Whose resistance increases with current will cause smaller increases in plate voltage as current decreases than would normally be the case, thus creating a non-linear relationship.

For simplicity of presentation, the device of the present invention has been particularly described in connection with a specific embodiment in which is employed a thyratron which will trip lwhen the voltages applied to the grids of the tube deviate from a straight line relationship and in which the tube will continue to discharge once the device has been tripped regardless of further changes in load conditions. Also, it has been assumed that the performance curve of the driving motor of the protected machinery will be a hyperbolic curve, which is the usual case, although conceivable, the eiiciency changes in the motor due to changes in line voltage might result in a substantially straight line performance curve.

In the specific embodiment, the thyratron, as

explained, is operating under a. D. C. voltage, butf,

if desired, an A. C. voltage could be applied for the same purpose, and, if desired, the switches QZ and 232 and solenoids 8l and 287 Could be replaced by a latching type of relay switch. Other methods of Vcombining or interpreting the voltages derived from the triodes as, for example, the substitution cf other types of tubes for the thyratron could, of course, lbe substituted within the skill of one versed in the art and, if desired, the devices Could be made to operate so that gradual inw crease or abrupt increases in load would not cause the device to trip or, if desired, the device could be utilized to energize the auxiliary electrical control if the motor load should fall below a predetermined level.

In the event that the characteristics of the thyratron or other tube substituted therefor are such that the relationship of applied voltages which will maintain equilibrium conditions or normal output is hyperbolic instead of straight line, it is of no consequence because in such event the development of the voltages responsive to current and voltage inputs may be modied to suit the characteristics of the tube. It is essential only that the voltages and current inputs to the motor of the protected apparatus which are normal; i. e., in accordance with the performance curve of the motor shall be translated intovolL- ages applied to the thyratron or other ilnal tube which nt the characteristics of such tube.

Other mcdiiications in the circuits of the device of the present invention also will be obvious to one skilled in the art. For example, in the preferred embodiment, the voltages derived across potentiometers M3 and 33 or 2MB and 233 are substantially non-fluctuating unidirectional voltages because of the rllter capacitors 39 and 3i and 23e and 23 i, resi'iectively. However, the circuit would function satisfactorily in the absence oi' such iilterinfr, or by a lesser degree of filtering, etc.

Also, in some cases, multi-tube amplification in place. of the single tube amplifier circuits may be found to be preferable. As will be apparent,

the sensitivity of the device can be readily increased to any desired extent merely by increasing the amount of amplication.

Also, for simplicity of presentation, the device has been'particularly described for use with a motor or other means operating on a single phase power supply. As will be readily understood, in the event of a polyphase pov/er supply, increased accuracy would lbe obtained by providing a current transformer in, and a voltage transformer across, each of the phases.

It thus will be seen that there has been provided, in accordance with the invention, a protective device which fully and accurately takes into account the changes in line voltage and line current of a device to be protected so that actuation of the protective mechanism very closely follows the actual load conditions on the device.

The apparatus is fully automatic in operation and `full protection of motors and apparatuses driven thereby from damage caused by improper load. conditions.

As many chang-es could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim as my invention:

l. A protective device for use with electrically operated means having a current input which increases hyperbolically with respect to decreases in voltage input under normal load comprising,

operated means having a current input and a voltage input which vary inversely to each other along a hyperbolic curve under normal load comprising, in combination, means for developing a rst voltage component increasing linearly in a positive direction with respect to increases in one of said inputs, means for developing a second voltage component opposed tothe rst voltage component which increases linearly in a positive direction with respect to increases along said hyperbolic curve in the other of said inputs, and means responsive to said voltage components for energizing a protective circuit when changes in said voltage components depart from a linear relationship corresponding to the inverse hyperbolic relationship of current and voltage inputs under normal load.

3.Y A protective device for use with electrically operated means having a current input and a voltage input which vary inversely to eachother ments forirec'eivil'ilV a plurality o f op'l'losedvolt-v 5 ages and constructed and arranged to discharge when aliincrement in one of said oppsedvoltages" in apositiv direction exceeds a; compen: sating decr'men a positive direction oi the other of said' oppose-o voltages", niearrsorieratively id connected to`h one element` of the tube for developing saidy one oi the' opposed voltages'in linear relationship' to one of saidinput's; andmeans' op-y eratively connected' tothe 'other element oi the` foi" developing`-tle other of Said Opposed voltages i'iij hyperbolic relationship to the other operated means Having' acurrent input and; aj

voltage input whichvary inversely to" each other 2:61

ojfsaid opposed voltages, mea-ris operatively oon--V :rr

riecte'd' to oneQleieiltof tire" tuloejA for developing one of saidv opposedvoltages' and' for varying Ysaid volta-ge lx1-'a posi e ldirec'ltiofn' inf increments hav'j ing aj "near relationship to" increasesjin one of sai'df inputs'and" mean operatively connected to' the otheri'ele'l' of thetuibe fol" developing the other' or said? opposedvol-tages'" and varying same in apositive direct-imiinA Saidjccmpensatin'g dec` reln'eritswlie the other orsaid-inputsvaries in:

creases in said one c'lf'tlfe inputs;

5i A loroteot'ive1 device for use with electrically' e operated means havingV a' current' and a" voltage inputr comprising; inf col nloinatin; aL protective circuit, means for energizing said"-circliit'conigli-isf"- ingf er ges`iil1e'jd-- tube having emporelements for receivinga-plura tyo'f opposed voltages a'ntljcon-l4 structe'dand alranged to discharge when' an' in: creieilt ino'r'le of Saidoppos'edfvoltage's in a posi:

tive' directio'l eiice'edsj af compensating decrement 50 iria positive direction offthe'other oi said opposed voltages, rifear'isf operatively connected to' one' e i* liie'rit4 ofjtlietube f or'developirieoneor said op: pose-d voltages-i amr for' varying saler voltage iii a' positivedirectie in' increments having a linear relatislipt crases'in oneiofvs'a'idinputs', and means operatlvelyconnectedto the other element of tl'ietubefor developing theother of'saidvclt-1 agesj'arldfol" varyingsal'ne in ai positive direction in'Y d'ecrelilerits` having al hyperbolic relationship'tcf 5d decreases?inl theotll'e'r`- of said inputs, thel amount ofsaid? decementsl-b'eing sufficientto 'compensate for said increments when-one of theinpfut's varies; approximately 'inversely tvithr'espectv to theoth'er o A protective f rl'evioefy for' use)v withJv ein'`r` elec;` trically operated inea"nsfA havingl a-v current inputva'r-ying in apredetermined hyperbclicv relation;- shipv Withl its voltage inputY under constantload veloping a; directr` current' voltage linearly pro' porti'oial to one'lofsaid? inputs, `secorldmeans for de'r'v'el'o'p'i'ng all;v o'iopnsed4 direct-f current' voltage" varyingAf said` predetermined; hyperbolic rela;

18 ajthyratron having elements operatively ccnl rected to said rst and second means, respectively, andadapted to discharge when said direct current voltal'res'A depart from a predetermined linear relationship, and a protective' circuit energized by the discharge of th'e thyratlon;

7.' A protectiveY device for use with an electric motor having avoltage input varyinginversely a predetermined hyperbolic relationship to the current input under normal load colnprisinga nrstcircuit for deriving a negative voltage component having a linear relationship to the curi :entv input tol the motor, said negative voltage oomponel'lt hecolll'ing less negative as the' cur-v rent increases; asecond circuit for deriving a' positive voltage' component varying in said pre# determined hyperbolic relationship to the voltage input,` s`ai d4 positive voltage component becoming more positive' as the voltage' increases, and a cir' cuit including a tuloeihaving elements operative: ly connected to' saidrst second circuits, rel spective'ly, and responsive to said voltage com- 'A ponents for protecting the motor when the changes irl s'aidfvoltage inputs depart from ,a

linear relationship,indicating said' variations in voltage and current inputs: under normal load.

8'.r A protectived'evice for use with electrically operated rrr'lealis;` having a .voltage and a current input'and adapted to beused inv combination vvi'thv the power supply lines of said means comprising, in combination", protective' circuit including' a thyratron having a control' grid' and a screen grid,

said tliyratrori being adapted' to' discharge when ailgfative voltage' onthe screen grid and a posi# tive voltage onth'e control grid depart from Ya predetermined linear relationship, a circuit for connection to; said lines and connected to said screen' grid' for impressing a negative voltage on said screen grid' having a linear relationship to versely in-` hyperbolicf relations'hip tof said iii-I' 41:?

tiie'otirer'y oi'seiri inputs".

operated liijeans having a current input anda voltage input whichvary inversely to eachrotl'lenri along a hyp e'rfpfolic' curvev under normal load coin- 9; A protective' device' ior use with electrically' prising, in",conlloil'latit'li-l`, 'r'st transformer means" forl dele'volping a secondary voltage increasing linearly in a positive direction with respect to` increases in one of said inputs, second trans'-` former means for developing a secondary voltage'V which increases' linearly in a positiveY direction With respe t to increases along'- said hyperbolic curve in the' otherof said inputs, and means re'- sponsivetosaid secondary voltages'for energizii'rlgV al protective circuito/heil changes inY said second'f ary voltages depart from' a linear relationship corresponding to; the'inve'rse' hyperbolic relation-, ship of current and voltage inputs under normal load. I Y

l0. Aj protective device forAv connection to the tive'directionl with' respect to increases in one ofI said Yi'nputst second transformer means for ill'-v` ducing a secondary voltage which increases linearly infa positive direction with respect to eloping'opposed' Voltages which vary linearly in a positive direction responsive to said secondary voltages, and means responsive to said opposed voltages for energizing a protective circuit when changes in said opposed voltages depart from a linear relationship corresponding to the inverse hyperbolic relationship of said current and voltage inputs under normal load.

11. A protective device for connection to the power lines of operated means having a current input and a voltage input which vary inversely to each other along a predetermined hyperbolic curve under normal load conditions comprising, in combination, a protective circuit, means for energizing said circuit comprising a tube having elements for receiving two opposed voltages and constructed and arranged to discharge when an increment in one of said opposed voltages in a positive direction exceeds a compensating decrement in a positive direction of the other of said opposed voltages, iirst means including a transformer for connection in one of said power lines for developing one of said opposed voltages in linear relationship to said current input, second means including a transformer for connection across the power lines for developing the other of said opposed voltages in hyperbolic relationship to said voltage input, and means operatively connecting the first and second means to the tube elements.

12. A protective device for connection to the power lines of electrically operated means drawing a line current which varies in hyperbolic relationship to the line voltage under constant load comprising, in combination, a step-up transformer and a step-down transformer having primaries for connection in series across the power lines and with theirl secondaries connected in opposition for developing a combined secondary voltage which varies hyperbolically in relationship to line voltage, a third transformer having a primary for carrying the line current and a secondary for developing a secondary voltage varying in direct linear relationship to line current, a tube having elements for receiving two applied voltages and constructed and arranged to discharge when said applied voltages depart from a predetermined linear relationship, means i'or amplifying and applying said secondary voltages to the elements of the tube and a protective circuit for the electrically operated means including said tube and constructed and arranged to function upon discharge of the tube.

13. A protective device for connection to the power lines of electrically operated means drawing a line current which varies in hyperbolic relationship to line voltage under constant load comprising, in combination, a protective circuit for said means, means for energizing said circuit comprising a tube having elements for receiving two opposed voltages and constructed and arranged to discharge when an increment in one of said opposed voltages in a positive direction exceeds a compensating decrement in a positive direction of the other of said opposed voltages, rst means for developing one of said opposed voltages in linear relationship to line current including a transformer having a primary for carrying line current and a secondary for developing a secondary voltage in linear relationship to said line current, second means for developing the other of said opposed voltages in hyperbolic relationship to said line voltage, said last named means including a step-up transforrnel` and a step-down transformer having primaries for connection in series across the power lines and with their secondaries connected in opposition for developing a combined secondary voltage which varies hyperbolically in relationship to line voltage, and means operatively connecting the said rst and second means to the tube elements.

14. A protective device for use with electrically operated means and adapted to be used in combination with the power supply lines of said means comprising, in combination, a first circuit adapted to be connected in one of said lines for deriving a first D. C. voltage component having a linear relationship to the current in said lines, a second circuit adapted to be connected to said lines for deriving a second D. C. Voltage component having a linear relationship to the voltage across said lines, a protective circuit for said means including a thyratron having a control grid and a screen grid adapted to be energized when a negative voltage on the screen grid and apositive voltage on the control grid depart from a predetermined linear relationship, a circuit operatively connected to the screen grid and including a triode having an element operatively connected to one of said first and second circuits and responsive to the D. C. voltage component derived thereby for impressing a negative voltage on said screen grid having a linear relationship to said voltage component, and a circuit operatively connected to the screen grid and including a triode having an element operatively connected to the other of said rst and second circuits and responsive to the voltage component derived thereby for impressing a positive voltage on said control grid having a hyperbolic relationship to said other D. C. voltage component.

15. A protective device for use with electrically operated means and adapted to be used in combination with the power supply lines of said means comprising, in combination, a first circuit including a transformer adapted to be connected in one of said lines and a rectifier for obtaining a negative D. C. voltage component having a linear relationship to the current in said lines, a second circuit including a transformer adapted to be connected across said lines and a rectifier for obtaining a negative D. C. voltage component having a linear relationship to the voltage across said lines, a protective circuit for said means including a thyratron having a control grid and a screen grid adapted to be energized when a negative voltage on the screen grid and a positive voltage on the control grid depart from a predetermined linear relationship, and circuits operatively connected to said grids and having means for impressing a negative voltage on said screen grid and a positive voltage on said control grid which vary in said predetermined linear relationship when the current in said lines varies substantially inversely in hyperbolic relationship with voltage changes across said lines, said last named means being operatively connected to the outputs of said rst and second circuits.

16. A protective device for use with electrically operated means and adapted to be used in combination with the power supply lines of said means comprising, in combination, a rst circuit including a transformer adapted to be connected in one of said lines and a rectiiier for obtaining a negative D. C. voltage component having a linear relationship to the current in said lines, a second circuit including a transformer adapted to be connected across said lines and a rectifier for obtaining a negative D. C. voltage component having a linear relationship to the voltage across said lines, a protective circuit for said means including a thyratron having a control grid and a screen grip adapted to be energized when a negative voltage on the screen grid and a positive voltage on the control grid depart from a predetermined linear relationship, a circuit operatively connected to the said screen grid and having means operatively connected to the said iirst circuit for impressing a negative voltage on said screen grid varying linearly in an opposite direction proportionately to changes in the rst named D. C. voltage component, and a circuit operatively connected to the said control grid and having means operatively connected to the said second circuit for impressing a positive voltage on said control grid varying hyperbolically in relationship to the second named D. C. voltage component whereby said grid voltages will vary in said predetermined linear relationship when the line current varies substantially inversely in hyperbolic relationship to changes in line voltage.

1'7. A protective device for use with electrically operated means and adapted to be used in combination with the power supply lines of said means comprising, in combination, a rst circuit including a transformen: adapted to be connected in one of said lines and a rectifier for obtaining a nega tive D. C. voltage component having a linear relationship to the current in said lines, a second circuit including a transformer adapted to be connected across said lines and a rectifier for obtaining a negative D. C. voltage component having a linear relationship to the current in said lines, a second circuit including a transformer adapted to be connected across said lines and a rectifier for obtaining a negative D. C. voltage component having a linear relationship to the voltage across said lines, a protective circuit for said means including a thyratron having a control grid and a screen grid adapted to be energized when a negative voltage on the screen grid and a positive voltage on the control grid depart from a predetermined linear relationship, a third circuit operatively connected to the iirst circuit and the screen grid having means responsive to the iirst named D. C. voltage component for impressing a negative voltage on said screen grid varying linearly in an opposite direction to changes in said component, a fourth circuit operatively connected to the second circuit and the control grid having means responsive to the lsecond named D. C. voltage component for impressing a positive voltage on said control grid varying hyperbolically in relationship to changes in said component, and means for adjusting the output of said circuits for predetermining the value of said grid voltages such that the grid voltages will vary in said predetermined linear relationship when the line current varies substantially inversely with changes in line voltage.

18. In a protective device for use with an electric motor and adapted to be connected to the power supply lines of said motor, the combination comprising a rst circuit for developing a D. C. voltage variable in proportion to changes in line voltage, a second circuit for developing a D. C. voltage variable in proportion to changes in line current, discharge means having a plurality of elements and adapted to function when the impressed voltage on said elements departs from a predetermined linear relationship, a circuit operatively connected to the rst circuit and one of said elements fo;1 developing one of said impressed voltages including a triode having a grid bias responsive to one of said developed D. C. voltages and having a predetermined plate load resulting in a linear relationship between the impressed voltage and said developed voltage, and a circuit operatively connected to the second circuit and the other of said elements for developing the other of said impressed voltages including a triode having a grid bias responsive to the other of said developed D. C. voltages and having a predetermined plate load such that the other of said impressed voltages will vary hyperbolically with respect to said other developed D, C. voltage.

i9. A protective device for use with electrically operated means and adapted to be used in ccmbination with the power supply lines of said means comprising, in combination, a iirst circuit comprising a transformer adapted to be connected in one of said lines, a rectifier, and a potentiometer for developing a first adjustable negative voltage proportional to line current, a second circuit comprising a transformer adapted to be connected across said lines, a rectifier, and a potentiometer for developing a second adinstable negative voltage proportional to line voltage, a protective circuit for said means including thyratron having a control grid and a screen grid and adapted to discharge when a predetermined pcsitive voltage impressed on said control grid exceeds a predetermined negative voltage impressed on said screen grid and when increments in a positive direction in one of said impressed voltages exceeds a proportionately related decrement in a positive direction in the other of said impressed voltages, an amplifying circuit operatively connected to the first circuit and the screen grid for impressing a negative voltage on said screen grid which varies linearly with respect to line current including a triode having a grid responsive to said rst adjustable negative voltage, a second amplifying circuit operatively connected to the second circuit and the control grid for impressing a positive voltage on said control grid which varies hy perbolically with respect to line voltage such that changes in line voltage which will cause unit changes in line current will cause uniform changes in the same direction in the impressed control grid voltage sufficient to balance changes in the screen grid voltage caused by such changes in line voltage including a triode having a grid responsive to said second adjustable negative voltage, and an adjustable source of a positive voltage bias connected to the grids of said triodes whereby the said predetermined voltages on said thyratron grids may be present by adjustment of said source and by adjustment of said potentiometers to correspond to a predetermined line voltage and current.

EVERETT C. BRILL.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Baker May 8, 1928 

